Fuel burner control using silicon controlled rectifier spark generation and thermocouple actuated reed switch



July 7, 1970 G. E. DIETZ 3,519,376

FUEL BURNER CONTROL USING SILICON CONTROLLED RECTIFIER SPARK 'GENERATIONAND THERMOCQUPLE ACTUATED REED SWITCH Filed May 24. 1968 GERALD E. DIETZINVENTOR.

AT TORNE K United States Patent 3,519,376 FUEL BURNER CONTROL USINGSILICON CONTROLLED RECTIFIER SPARK GENERA- TION AND THERMOCOUPLEACTUATED REED SWITCH Gerald E. Dietz, Milwaukee, Wis., assignor to PennControls, Inc., Oak Brook, Ill., a corporation of Delaware Filed May 24,1968, Ser. No. 731,822 Int. Cl. F23q 3/00 U.S. Cl. 431-43 7 ClaimsABSTRACT OF THE DISCLOSURE Gaseous fuel is fed through anelectromagnetically actuated main valve to a main burner for ignitionthereat from a standing pilot flame, under conditions where the pilotflame is sensed by a thermocouple. The thermocouple generates suflicientcurrent to actuate magnetically a reed switch to closed condition toenergize the main valve. Under conditions where the pilot flame isextinguished inadvertently, the reed switch, after the thermocouple hascooled sufliciently reopens the energizing circuit of the main valve,stopping the flow of fuel to the main burner. Simultaneously, thethermocouple actuated reed switch, in reopening, activates a sparkgenerator, The generator provides a continuous high voltage spark bymeans of a silicon controlled rectifier oscillating circuit forrelighting the pilot flame. When the pilot flame is successfully relitand the thermocouple reheated, the reed switch contacts again close,simultaneously deenergizing the spark generator circuit and preparingthe main valve for reenergization through thermostat contacts, upon thenext successive call for heating. Two embodiments are disclosed, one foroperation from a 120 volt alternating power source and the other foroperation from a 25 volt alternating power source; both utilizing thesame silicon controlled rectifier oscillator circuit for sparkgeneration.

The invention relates to fuel burner controls and, more particularly, tosuch a control for automatically generating a high voltage electricspark for igniting a pilot flame, under conditions where such flame isinadvertently extinguished, while simultaneously causing deenergizationof main burner fuel feeding means.

Fuel burners are often located in difficult to reach locations. Forexample, infrared heaters are sometimes located high in ceilings ofshops or plants. In such situations fuel at the main burner is often litthrough a standing pilot flame. In the event of inadvertent outage ofthe pilot flame (due to wind gusts or a momentary interruption of thegas supply), it is desirable that the main burner fuel feeding mechanismbe quickly caused to shut off the fuel supply to the main burner. At thesame time relighting of the pilot flame should be automatically andquickly initiated. It is also desirable that such an automatic safetycontrol be economical to manufacture and maintain and be substantiallytrouble free.

It is, therefore, an object of the invention to provide a fuel burnercontrol system in which a standing pilot ignites fuel at a main burner,which control monitors the pilot flame and provides automatic electricreignition thereof 3,519,376 Patented July 7, 1970 in case of outage,while simultaneously shutting off fuel fed to the main burner.

It is also an object of the invention to provide such a control which,upon successful relighting of the pilot flame, effects simultaneousdeenergization of the electric ignition means for the pilot andreenergization of the fuel feeding means for the main burner through asingle pair of electrical contacts.

The invention involves providing a thermocouple in position to monitorthe pilot flame. The thermocouple, when sufliciently heated,magnetically energizes a reed switch to closed position. The reed switchcontacts control energization of main burner fuel feeding means and anelectric spark generator. The electric spark generator comprises asilicon controlled rectifier oscillator, utilizing capacitor dischargethrough its anode-cathode circuit to pulse the primary winding of a highvoltage spark transformer. The transformer provides a continuous sparkacross a pair of spaced apart electrodes for igniting the pilot flame.The pilot flame is sensed by the thermocouple which causes the reedswitch contacts to be closed. Closing of the contacts simultaneouslyenergizes the fuel feeding means of the main burner, while applying ashort circuit between the gate and cathode electrodes of the siliconcontrolled rectifier of the oscillator. Such short circuit places the0scillator in nonoscillating condition, shutting down the sparkgenerator.

Features and advantages of the invention may be seen from the above,from the following description of the preferred embodiment whenconsidered in conjunction with the drawing and from the appended claims.

In the drawings:

FIG. 1 is a simplified, schematic wiring diagram of a fuel burnercontrol using a standing pilot flame for igniting fuel fed to a mainburner and utilizing an electric continuous spark generator for lightingthe pilot flame, and embodying the invention; the control being arrangedfor operation from a volt alternating power source; and

FIG. 2 is a simplified, schematic wiring diagram of another embodimentof the invention similar to that of FIG. 1, but operable from a 25 voltalternating power source.

With reference to the preferred embodiment of FIG. 1, 12.0 volts at 60cycles per second from any convenient source (not shown) is applied tothe circuitry over supply lines L1, L2. A main gas valve, generallydesignated MGV, is shown diagrammatically as being of theelectromagnetic actuated type, having an actuating coil SEL. When coilSEL is energized, the valve opens permitting the flow of gaseous fuelfrom gas inlet IP to gas outlet OP, as indicated by directional arrows,for supplying fuel to a main burner (not shown) for ignition thereatfrom a standing pilot flame. The standing pilot flame is designated FL,fuel being supplied therefor through a manual rotorcock RC, controllingthe flow of pilot fuel through a gas line GL.

A thermocouple TC is positioned to be heated by pilot flame FL and isconnected across an energizing coil RSW of a reed switch indicated inbroken line outline as RS. Reed switch RS includes a pair of normallyopen contacts RSC connected in series with main valve actuating coil SELand a pair of thermostat contacts T positioned in the space to beheated, the series circuit being connected across supply lines L1, L2through manual line switch MS.

Means for generating a continuous spark for igniting fuel at the pilotis provided. This spark generator includes a silicon controlledrectifier SCR connected in an oscillating circuit for pulsing theprimary winding PR of a. high voltage spark transformer, generallydesignated ST. The secondary winding SEC of high voltage sparktransformer ST is connected across a pair of spaced apart electrodes,designated SG, positioned to ignite fuel at the pilot outlet. RectifierSCR (having an anode a, a cathode c and a gate g electrodes) has itsanode electrode a connected through a diode D2 in series with a currentlimiting resistor R3 and switch MS to supply line L2. Its cathodeelectrode c is connected through a resistor R2 to a point intermediatereed switch contacts RSC and main valve actuating coil SEL. Anotherresistor R1 is connected shunting the anode-cathode circuit of rectifierSCR, the shunted circuit including resistor R2, diode D2 and resistorR3. A second diode D1 is connected between the cathode c and gate gelectrodes of rectifier SCR so as to permit current flow only from thecathode c to gate g electrodes. A charging capacitor C is connected inseries with primary winding PR of sparking transformer ST from the gateg to anode a electrodes of rectifier SCR in the named order.

In operation, assume that line switch MS is closed, applying power tothe circuit, While rotorcock RC is manually rotated to permit the flowof gas through line GL to the pilot outlet. As the voltage on supplyline L2 becomes positive with respect to supply line L1, capacitor Ccharges to fully charged condition through line switch MS, resistor R3,diode D2 and primary winding PR to supply line L1. As supply line L1becomes positive with respect to supply line L2, during the start of thenext negative half cycle of the applied power, the potential at gateelectrode g of rectifier SCR with respect to its cathode electrode (thepotential appearing across diode D1) becomes sufliciently positive tocause rectifier SCR to conduct through its anode-cathode circuit,discharging previously charged capacitor C through primary winding PR ofthe high voltage spark transformer ST. Such pulsing of primary windingPR causes generation of an output spark across spark gap SG to ignitethe pilot flame.

Next assume that thermocouple TC senses the pilot flame FL and is heatedsufliciently to generate enough current to actuate reed switch RS bymeans of its energizing coil RSW. Switch RS closes its contacts RSC,applying a relatively low impedance path across diode D1. This lowimpedance path prevents the development of a sulficient voltage acrossthe gate-cathode electrodes of rectifier SCR to fire the rectifier.Rectifier SCR is thus maintained in nonconducting condition, stoppingthe spark generator oscillator circuit from generating sparks across gapSG.

It may be noted that, until reed switch contacts RSC are actuated closed(by the sensing of the pilot flame by the thermocouple TC) capacitor Ccharges every positive half cycle of the applied voltage and dischargesat the start of each negative half cycle of the applied voltage,producing a spark at spark gap SG once every negative half cycle of theapplied voltage.

As reed switch contacts RSC close, they also prepare an energizingcircuit for the actuating coil SEL of main gas valve MGV, preparing themain gas valve for operation subject to a call for heat from thermostatT.

Next assume that heat is called for by the closing of standing pilotflame FL is inadvertently extinguished. Under such condition, asthermocouple TC cools sufiiciently, insuflicient power is applied toactuating coil RSW of reed switch RS to maintain reed switch contactsRSC closed. Contacts, RSC, thus, return to their normally opencondition, interrupting the energizing circuit of coil SEL of main gasvalve MGV. Main gas valve MGV closes, shutting off the supply of fuel tothe main fuel burner (not shown) which is, thereby, extinguished.Simultaneously, this reopening of contacts RSC removes the low impedancepath previously applied between the gate g and cathode c electrodes ofsilicon controlled rectifier SCR. Under such conditions, as waspreviously described, the spark generator immediately again provides acontinuous spark every negative half cycle of the applied voltage acrossspark gaps SG to relight the pilot flame FL.

Next assume that the pilot flame is relit, reheating thermocouple TCsufiiciently to reclose reed switch contacts RSC, thereby causingreenergization of main gas valve MGV and stopping the spark generator,as was previously described.

The embodiment of FIG. 2 operates exactly the same as that of FIG. 1with the exception that, instead of voltpower, power at the relativelylow voltage of 25 volts, 60 cycles per second may be applied from anyconvenient source (not shown) to the circuitry over supply lines L1, L2.This 25 volt, 60 cycle power is transformed by TR to 120 volt power forthe spark generator. Transformer TR has a primary winding PR-l connectedacross supply lines L1, L2 through line switch MS, and a secondarywinding SE connected to supply line L1 at one end and at its, other endto the right hand side of resistor R3 in the anode circuit of siliconcontrolled rectifier SCR. Transformer TR is wound to provide thepolarities indicated by the dots. In addition, a second capacitor C2 isconnected between the anode of diode D1 and the right hand end ofresistor R2 in the cathode circuit of rectifier SCR. With thisarrangement the spark generator oscillator of rectifier SCR is suppliedwith a steppedup voltage of 120 volts by transformer TR, as in the FIG.1 embodiment, but is triggered (through resistors R1 and R2 and diode-D1) at 25 volts; the voltage at which the main gas valve MGV isoperated in this embodiment. This beneficially enables the samecontinuous spark generator to be utilized in a gas control using a 25volt actuated gas valve and one using a 120 volt actuated gas valve, asin FIG. 1.

The circuit operation is the same as that previously described for theFIG. 1 continuous spark generator with reed switch contacts RSCfunctioning exactly the same to provide a low impedance path across thegate-cathode electrodes of rectifier SCR to stop continuous sparkgeneration, under conditions where thermocouple TC is heatedsufliciently by pilot flame FL.

The remainder of the FIG. 2 circuit operation is exactly the same asthat of the FIG. 1 circuit with the exception that transformer TRprovides across its winding SE the voltage polarity which causes, whenresistor R3 is positive with respect to the cathode c of rectifier SCR,capacitor C1 to charge through resistor R3, diode D2, primary windingPR, to line L1. Under conditions where the voltage applied by secondarywinding SE to resistor R, becomes negative with respect to the voltageapplied to the gate electrode g of rectifier SCR, rectifier SCR fires,causing capacitor C1 to discharge through primary winding PR in theanode-cathode circuit of rectifier SCR, pulsing the primary winding PRand causing a spark across gap SG.

Capacitor C2 is provided between resistor R2 and the cathode electrode cof rectifier SCR to isolate reed switch contacts RSC from rectifier SCRto insure that, when the reed switch contacts close, the siliconcontrolled rectifier is maintained in nonconducting condition.

Satisfactory operation was obtained in one tested embodiment of the FIG.1 circuit using the following components: resistors R1 and R2 atkilohms, resistor R3 at 150 ohms, capacitor C at 1 microfared andrectifier SCR of the GEC106B type.

Satisfactory operation was obtained in one tested embodiment of the FIG.2 circuit utilizing the following circuit components: resistor R1 at 4.7kilohms, resistor R2 at 1.5 kilohms, resistor R3 at 270 ohms, capacitorC1 at 1 microfarad, capacitor C2 at .33 microfarad and rectifier SCR ofthe GEC106B type.

It may be noted that with either embodiment of the subject control asingle pair of reed switch contacts (RSC) are utilized to control sparkgeneration and actuation of main valve MGV, thereby providing anefficient automatic burner control.

As changes can be made in the above described construction and manyapparently different embodiments of this invention can be made Withoutdeparting from the scope thereof, it is intended that all mattercontained in the above description or shown on the accompanying drawingbe interpreted as illustrative only and not in a limiting sense.

What is claimed is:

1. A control for a fuel burner system having a main burner comprising:

fuel feeding means operative when energized for causing fuel to flow tosaid main burner for ignition thereat,

pilot flame means positioned for transferring ignition from the pilotflame to said main burner,

an electric igniter means operative for lighting said pilot flame,

a thermocouple positioned for monitoring said pilot flame for generatingcurrent when heated by said pilot flame,

thermostat means for calling for energization of said fuel feedingmeans,

a single pair of normally open contacts in series with said thermostatmeans for causing energization of such fuel feeding means through saidthermostat means under conditions where said contacts are actuatedclosed,

magnetic actuating means responsive to said thermocouple for actuatingsaid normally open switch con tacts to closed condition when energizedsufficiently by said thermocouple current,

said single pair contacts when actuated closed preventing operation ofsaid igniter means while automatically causing reoperation thereof whenin open condition.

2. A control as set forth in claim 1 wherein said electric igniter meansincludes a pair of spaced apart electrodes positioned for igniting saidpilot flame, and

continuous spark generating oscillating means for providing at said pairof spaced apart electrodes a continuous igniting spark for said pilotflame.

3. A control as set forth in claim 2 wherein said pair of normally opencontacts and said magnetic actuating means comprise:

thermocouple responsive reed switch means including i normally open reedswitch contacts and magnetic actuated coil means connected forenergization by said thermocouple for causing closing of said reedswitch contacts under heated conditions of said thermocouple.

4. The control as set forth in claim 3 wherein said spark generatingmeans comprise a silicon controlled rectifier having anode, cathode, andgate electrodes,

a first diode connects said cathode electrode to said gate electrodepermitting current flow only from the cathode to gate electrodes,

a second diode connected in the anode circuit of said silicon controlledrectifier for providing half-wave rectified power thereto from analternating power source,

an ignition transformer having a primary winding and a secondarywinding, said secondary winding being directly connected across saidspark electrodes positioned for igniting said pilot flame,

said primary winding being connected in series with a capacitor acrossthe anode-gate circuit of said silicon controlled rectifier forproviding high voltage pulses through said primary winding for ignitingsaid pilot flame under conditions where said capacitor dischargesthrough said silicon controlled rectifier,

said reed switch contacts being connected between the cathode and gateelectrodes of said silicon controlled rectifier for providing a lowimpedance shunt path therebetween for maintaining said rectifier innonoscillating condition under conditions where reed switch contacts areclosed for energizing said fuel feeding means.

5. A control as set forth in claim 4 wherein step-up transformer meansare provided between said applied power and said silicon controlledrectifier oscillating means for providing a predetermined increasedvoltage energization of said oscillator under conditions where said fuelfeeding means is operable at the lower input voltage to said stetruptransformer means.

'6. A control for a main fuel burner comprising:

a pilot burner,

a thermocouple positioned in the flame of said pilot burner forgenerating current when heated,

fuel feeding means operative when energized for causing fuel to flow tosaid rnain burner for ignition thereat by said pilot flame,

means for calling for energization oof said fuel feeding means,

a silicon controlled rectifier having anode, cathode and gateelectrodes,

a pair of normally open electrical contacts,

means responsive to current generated by said thermocouple for actuatingsaid contacts closed under heated conditions of said thermocouple andfor returning said contacts to open condition under cold conditions ofsaid thermocouple,

said fuel feeding means being connected in series circuit with saidcontacts for energization from an alternating power source in responseto said means calling for said energization,

said silicon controlled rectifier having its said cathode electrodeconnected through a resistor to a point intermediate said contacts andsaid fuel feeding means in said series circuit,

said rectifier having its anode-cathode circuit connected through afirst diode and said contacts across said alternating power source forapplying unidirectional power through the anode-cathode circuit of saidrectifier through said contacts,

said gate electrode of said rectifier being connected shunting saidcontacts,

said gate electrode also being connected to the anode electrode of saidrectifier through a capacitor,

a second diode having an anode and cathode with its anode electrodeconnected to said rectifier cathode and its cathode electrode connectedto the gate electrode of said rectifier,

ignition transformer means having primary and secondary windings,

said primary winding being connected in series with Eaid capacitor inthe gate-anode circuit of said rectithe said secondary winding of saidignition transformer being connected across a pair of electrodes spacedapart and in a position to ignite fuel at said pilot burner, underconditions where said energization calling means calls for energizationof said fuel feeding means,

said thermocouple means causing, under conditions of being heatedsufficiently by said pilot fuel burner, actuation of said contacts toclosed condition for energization of said fuel feeding means andsimultaneously providing a low impedance path across the gate-cathodecircuit of said rectifier maintaining said rectifier in nonfiredcondition.

7. A control as set forth in claim 6 wherein said pair of normally openelectric contacts and means for actuating said contacts closed comprisea reed switch having a pair of normally open contacts and a magneticactuating coil connected for energization by said thermocouple means.

References Cited UNITED STATES PATENTS EDWARD G. FAVORS, PrimaryExaminer US. Cl. X.R.

